Though most posters here doubt that we have a shot at Zach Parise in free agency this summer, many have mentioned that they would love to have him on the Caps even at $7.0-8.0M a year as a replacement for Alex Semin. After performing some objective analysis of Semin and Parise's career statistics I can't accept that Parise represents as much of an upgrade to Semin as most posters here seem to think he might. Obviously there are some problems with a purely statistical approach; hockey games are not played on paper, and boxcar stats often fail to capture certain facets of a hockey player's value. The fact is, however, that both Semin and Parise are paid for their production; If Parise is really worth 2.5-3.0M dollars more than Semin, I would expect it to show at least a little bit in their career statistics.

There is no doubt that, all things being equal (salary, contract length, age, injury status etc), Zach Parise is a more valuable hockey player than Alex Semin. However, the gap between their values is not as wide as you might think, and ultimately it is really only intangible factors that account for this difference. As far as hockey skill, scoring output and potential go, there is actually very little to choose between the two players, and one might even argue that Semin has a higher absolute ceiling (best possible season/level of play) than Parise.

Both players have 1984 birthdays, though Semin (13th overall 2002 Entry Draft) was taken 1 year earlier than Parise (17th overall 2003 Entry Draft), and both players have played in 7 NHL seasons, though some have been shortened by injury for both players. This means that a direct comparison of career stat lines offers a relatively fair first blush metric of player quality.

Notes:
Parise has scored 2 more points in 33 more games.
Semin's PPG is 0.87, Parise's PPG is .815.
Over a season that prorates to 71.4 pts vs 66.42.
Goal/Assist ratios are almost identical.
Semin pts/60 2.98, Parise pts/60 2.70.
That is a 10% difference between their scoring rates per 60 minutes, which actually is somewhat significant.
If Parise comes to the caps, his icetime would likely be around what Semin's is. Projected point total with this metric is actually 64.5 pts.
But maybe, you argue, this comparison is unfair. Zach's played a full year in his first season, whereas Semin only played 52 in his first season. Furthermore, Zach has played better "recently".

Lets look at a season by season breakdown of Parise vs. Semin starting with their last two seasons:

Here we see why Parise's value is higher than Semin's in most people's minds; though both players have underperformed to a certain extent, most people, including myself, are much more willing to give Parise a pass for the recent decline in his production because he was injured in the 2010-2011 season. Some people might be inclined to ignore Parise's 2010-2011 statline entirely and use his 2009-2010 statline for analysis instead. This is not entirely unfair, but I think it's important to remember that Semin and Parise had near identical numbers in that season. In any case, lets look at Semin/Parise's last 2 years, just for the sake of argument:
Semin and Parise have actually played a similar number of games minutes in the last 2 years. Semin - 2468 Parise - 2020.
The games discrepancy is obviously a bit larger (95 vs 142), but not entirely incomparable.
Semin - 108p, Parise - 75p
Semin - .75 ppg, Parise - .78 ppg
Semin - 2.63 - points per minute, Parise - 2.22
As mentioned before, we are being somewhat uncharitable to Parise by including his injury season over his 2009-10, but I don't think that this means that the above analysis can be entirely disregarded. The fact of the matter is that Semin has actually scored at a slightly higher per minute rate than Parise over the last two seasons.

Notes:
Here we get some more insight into why Parise is considered the more valuable player; Parise's best three seasons have been his last three (injury-free) seasons.
Parise has scored more points in his best seasons (Parise - 245, Semin - 236).
Parise also scored more points in his best season than Semin did in his best season (Semin - 84, Parise - 94).
Semin, however, has the edge in per game totals, both in total(Semin - 1.11, Parise 1.00) and in a single season (Semin - 1.27, Parise - 1.14).
Semin's average over his best 3 is only .03 ppg Zach's abosolute best.
I won't even get into points per minute...
Though we have examined some of the reasons that people rank Parise ahead of Semin, most of our analysis thus far has explicitly aimed at demonstrating that Semin is at least a comparable player. To preempt any attacks on this analysis, I will now examine some metric's that clearly work in Parise's favor.

This looks very bad for Semin... Not only are his point totals lower, but they came in the last two years.
Some, but certainly not all, of this can be attributed to reduced ice time and terrible power play performance.
To be fair to Semin, we note that the per game totals are pretty similar.
Career Playoffs Statline:

This doesn't look nearly as bad for Semin.
Both players have performed below expectations to a certain extent in the playoffs.
The only really fair way to compare the two is ppg, and its pretty close (Semin - .66, Parise - .70)
Semin was actually ahead before this season, where washington played very defensively, and Semin put up only 4 points in 14 games.

In Conclusion:

The point I am trying to make is not that Alex Semin is better than Zach Parise, or even that he is just as good as Zach Parise. As I said before, If I were building a team and I had to choose between Parise and Semin with all things being equal, I would probably take Parise without thinking too hard about it. I am of the opinion, however, that the difference in their values, though non-trivial, is not that large. That is, I would take Semin on a $4.5-5.0M contract over Parise on a $7.0-7.5M contract in a heartbeat.